Avoid saturation of hBWE_FD->old_input_wb_fx signal. Add missing assignment...

Avoid saturation of hBWE_FD->old_input_wb_fx signal. Add missing assignment st_fx->Q_old_wtda = Q_wb_sp and clear parts of hBWE_FD->L_old_wtda_swb_fx that are unused to avoid that these sample overflow during rescale elsewhere later.